Using viral vectors to introduce foreign deoxyribonucleic acid (DNA) into a eukaryotic cell is a well-established technique in the fields of biotechnology, life science research and gene therapy. However, whether foreign DNA is successfully introduced into a cell highly depends on the efficiency of the viral infection/transduction which in turn is influenced by various parameters such as the type of virus and cell. To increase infection efficiency, additives are used, as for example recombinant human fibronectin fragment CH-2961 so-called RetroNectin® (Takara; TAK T100). RetroNectin® recombinant human fibronectin fragment is a chimeric peptide of recombinant human fibronectin fragments produced in E. coli. It contains 574 amino acids with a molecular weight of 63 kDa. When coated on the surface of cell culture chambers such as culture dishes, petri dishes, flasks or bags, RetroNectin® recombinant human fibronectin fragment enhances retrovirus-mediated gene transduction into mammalian cells. This enhancement is thought to be due to co-localization of retroviral particles and target cells at the site of RetroNectin® recombinant human fibronectin fragment. RetroNectin® recombinant human fibronectin fragment binds to virus particles via interaction with the heparin-binding domain II, and to cells mainly through interaction of the cell surface integrin receptor Very Late Antigen-4 (VLA-4) with the fibronectin Connecting Segment 1 peptide (CS1) site. Additionally, cells may also bind through the interaction of another fibronectin ligand within the central cell-binding domain with a corresponding integrin receptor Very Late Antigen-5 (VLA-5) on the cell surface.
The production of RetroNectin® recombinant human fibronectin fragment is elaborate and cost intensive, since the artificial protein is relatively large. In addition, it has to be coated on culture dishes, making the application time and labour intensive. Moreover, RetroNectin® recombinant human fibronectin fragment can not be applied to improve infection of those types of cells, as e.g. some kind of stem cells, which immediately start to differentiate upon plating and thus have to be kept in suspension.
An alternative approach for supporting viral infection of cells was suggested after the discovery that HIV infection in vivo is supported by semen. The infection supporting properties could be attributed to a 38 amino acid fragment of prostatic acidic phosphatase (PAP248-286) which was named semen-derived enhancer of virus infection (SEVI) (Münch et al., 2007). SEVI was shown to support viral infection in vitro probably due to forming amyloid fibrils, which are thought to interact with both, the viral envelope and the cell membrane (Brender et al., 2009). Although SEVI displays viral infection supporting properties, its technical applicability is rather limited. The lyophilized fragments of prostatic acidic phosphatase (PAP) have to be dissolved in solutions of neutral pH and distinct salt concentrations and must be agitated at 37° C. for about 1 to 3 days (Münch et al., 2007, Roan et al., 2009, Roan et al., 2010). Thus, SEVI is not suitable for use in high throughput biotechnological or life science applications. Therefore, novel means and methods are required to efficiently enhance viral infection of cells, which are easy and inexpensive to provide and convenient to apply.